The present invention relates to the improvement of a navigation apparatus for vehicles, which has the function of displaying the current position, travelling direction, etc of the vehicle with a map image overlapped on the screen of such a display device as CRT display.
Such navigation apparatuses are generally designed to display on a CRT screen map information stored in a large-capacity storage device, such as a CD-ROM. Examples of the types of the map information include the courses, names, lengths, and directions of roads, the names of the places along a road, the locations and names of intersections, and the locations or names of buildings. These map information are incorporated in the vehicle and hence can be called "internal road information".
Navigation systems having means for receiving traffic information through the radio are also known. In this navigation system, all the traffic information that can be displayed presently is displayed on a CRT screen in accordance with the data received by the reception means (this data being hereinafter referred to as "external road information") and the internal road information. Such a navigation system is disclosed in, for example, Japanese Kokai No. 63-231477.
When all the internal road information, or all the internal and external road information, related to the travel of the vehicle is displayed on the screen of a display portion, as in the case of the aforementioned conventional examples, the amount of information displayed on the screen becomes too much and the visibility of the necessary information is deteriorated, although abundant information can be offered to the driver. For example, the traffic information about the roads in the opposite direction to that in which the vehicle is currently travelling is basically unnecessary for the driver.